1. Field of the Invention
The present invention relates to an imaging apparatus control unit that controls operations for ordering an imaging apparatus, such as a digital camera, to carry out automatic sequence photography.
2. Description of the Related Art
A digital camera, which can carry out automatic sequence photography, is known. When automatic sequence photography commences with the depression of a release button, a plurality of sequential photographs are automatically taken, differently from the case of single photography where a single photograph is taken.
A photograph is taken in a digital camera by generating an image signal corresponding to the optical image of an object received by an imaging device, carrying out predetermined signal processing on the image signal by a signal processor, and storing the image signal in a memory. As shown in FIG. 3, single photography is completed by storing the singular generated frame of an image signal in a temporary memory, carrying out the predetermined signal processing on the stored image signal, and storing the image signal in the main memory, in order. Incidentally, in the timing chart of FIG. 3, each operation is carried out during a period of a standing pulse. Accordingly, if sequential photographs are taken by a user's repetition of the single photography, one frame of an image signal starts to be generated after the previous frame of an image signal has been stored in the main memory.
On the other hand, if sequential photographs are taken in automatic sequence photography, storing a plurality of frames of the generated image signals to the temporary memory, predetermined signal processing on the stored image signals, and storing the image signals in the main memory is carried out overlappingly, as shown in FIG. 4. For example, first a first image data (see “D1” in FIG. 4) is generated and stored in the temporary memory, next a second image data (see “D2” in FIG. 4) is generated and stored in the temporary memory while the first image data undergoes predetermined signal processing and storage in the main memory. Since then, subsequent image data is generated and stored in the temporary memory while previously generated image data undergoes predetermined signal processing and storage in the main memory. Accordingly, the sequential photographs can be taken quickly by concurrently carrying out a plurality of operations in automatic sequence photography.
In the automatic sequence photography described above, not all of the generated image signals corresponding to sequential photographs can be stored in the main memory once the main memory becomes full. The storage failure is problematic. In addition, the power consumption for driving a shutter, generating an image signal, and undergoing predetermined signal processing is excessive.
On the other hand, it is desired to make use of the spare capacity of the main memory upon the completion of the automatic sequence photography. Consequently, the time until depletion of the spare capacity is estimated, and the generation of the image signal is terminated before the estimated time, thus avoiding the storage failure.
By the way, a raw image signal generated by an imaging device is compressed according to variable-length compression, for example JPEG, because the amount of data required for a raw image signal is large. As for compressing raw image signals of different optical images, data sizes between compressed image signals may vary with each other even if the data required for the raw image signals are the same. The different size requirements result from variation of contrast and spatial frequency in photographed optical images. Consequently, it is impossible to estimate an accurate typical data space required for one frame of an image signal, making it difficult to estimate the time until depletion of the spare capacity of the main memory.
For the above problem, a maximum data size of a compressed image signal is estimated statistically. The maximum data size is determined from the typical data size of one frame of an image signal. When the spare capacity becomes less than the maximum data size, the auto sequence photography is complete. However, the main memory still may have excess capacity after automatic sequence photography, because it is rare that the data size of a practically compressed image signal equals the statistically estimated maximum data size. It is problematic when automatic sequence photography is completed with remaining spare capacity because a user usually desires to take as many photographs as possible in automatic sequence photography.
Further for the above problem, it is suggested that an upper limited data size of an image signal is predetermined. All of the generated image signals are surely stored in the main memory by compressing an image signal, of which data size is under the upper limited data size, with a lower compression ratio and compressing an image signal, of which data size is over the upper limited data size, with a higher compression ratio. However, it is problematic that an image quality gets deteriorated due to compressing with a higher compression ratio.